A sample taken from the surface of a leaf contains bacterium B and several other species of bacterium. Bacterium B forms blue colonies on nutrient agar. The other species form cream colonies.
The sample was added to two sterile culture media. The results after incubation are shown in the table.
| Culture medium | Result |
|---|---|
| Nutrient agar plate P | Separate blue colonies and separate cream colonies |
| Nutrient broth in flask Q | A mixture of bacterium B and the other species |
The scientist needs to grow bacterium B without the other species.
Suggest why the scientist should use material from one blue colony on plate P to start a new culture, rather than use material from flask Q.
Three technicians attempt to grow bacterium B in sterile nutrient broth in flasks R, S and T.
After incubation, a sample from each flask is spread onto a separate sterile nutrient agar plate. The results are shown in the table.
| Flask sampled | Result on nutrient agar |
|---|---|
| R | Separate blue colonies only |
| S | Separate blue and cream colonies |
| T | No colonies |
The scientist will retain one flask and discard the other two.
Suggest which flask should be retained. Explain why the other two flasks should be discarded.
The scientist uses a sterile inoculating loop that has been allowed to cool.
The table shows four possible procedures for transferring bacterium B into nutrient broth.
| Procedure | Flask and nutrient broth | Time the flask is left open |
|---|---|---|
| W | Sterilised | A few seconds |
| X | Sterilised | 10 minutes |
| Y | Not sterilised | A few seconds |
| Z | Not sterilised | 10 minutes |
Suggest which procedure the scientist should use. Explain your answer.
282 exam-style questions on AQA GCSE Biology 1.1 Cell structure, covering 1.1.1 Eukaryotes and prokaryotes, 1.1.2 Animal and plant cells, 1.1.3 Cell specialisation, 1.1.4 Cell differentiation, 1.1.5 Microscopy, and 1.1.6 Culturing microorganisms. Each one has a worked solution and a mark scheme showing where the marks go.